1. Field
The described aspects relate generally to systems and methods for reselecting and handing over a mobile communication device from a first cell to a second cell in a cellular wireless communication system. In particular, the described aspects relate to criteria for selecting a second cell while a mobile device is on or otherwise interacting with and/or controlled by a first cell.
2. Background
Cellular wireless communication systems generally comprise a number of radio transceivers, or base stations, that define service areas or cells. The schematic diagram in FIG. 1 illustrates a system 100 comprising four base stations 120 defining respective cells 110. The cells typically overlap in order to ensure continuous coverage of service in the service area. Cellular systems are designed specifically to accommodate users as they move around within the system. Thus, mobile communications devices 130 may interact with various base stations as the devices move through the respective cells 110 of the system 100.
As a mobile station is moved from the service area defined by one cell into that defined by another, the system and the mobile station must break the connection with one base station and establish a connection with another base station while minimizing the connection loss between the mobile station and the system. This operation is sometimes known as a cell reselection, a handoff or a handover. The term “camped on” is commonly used, and will be used hereinafter, to describe the base station with which, and respective cell in which, a mobile station is operating. That is, a cell reselection involves a mobile station moving from being camped on one cell to being camped on another cell.
Typically, a cell reselection can be initiated either by the mobile station or by the cellular system. How reselection is initiated can depend on factors such as the kind of cellular system, its mode of operation and on the capabilities of a mobile station. In any event, reselection is typically initiated either as a result of a service degradation, which tends to lead to increased power consumption requirements, or there being an opportunity to improve the service, which would lead to reduced power consumption requirements. Especially since many mobile stations operate from battery power, an opportunity to reduce power consumption, thereby improving power efficiency, is usually advantageous. Service degradation can result from factors such as increasing distance between a mobile station and a base station or natural or man-made obstructions such as hills or buildings, respectively.
One known kind of reselection operation requires a mobile station to monitor the signaling level of cells that neighbor the cell (NCELLs) on which the mobile station is camped, which will be referred to hereinafter as the “serving cell”. Such reselection operation compares the monitored signaling levels of the NCELLs with the signaling level of the serving cell. Then, if the signaling level of a NCELL is deemed by the mobile station to be better than that of the serving cell, for at least a predefined period of time (say, five seconds), the mobile station initiates a reselection to the respective NCELL, which becomes the new serving cell.
The reselection operation discussed above initiates reselection based upon the NCELL's signaling level. Thus, a mobile device may be handed over to a NCELL with a stronger signaling level but having a poor signal quality, resulting in a dropped call.